dynamic positioning conference october 15-16,...

Author’s Name Name of the Paper Session

DYNAMIC POSITIONING CONFERENCE October 15-16, 2013

POWER SESSION

The Case for Simplicity

By Sean M. Hickey

Loch Caillte Consulting

Owner

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Sean M. Hickey Power The Case for Simplicity

MTS DP Conference - Houston October 15-16, 2013 Page 1

The Case for Simplicity

Abstract

With a personal perspective beginning in 1977 with the design and construction of DP drilling rigs, DP construction

vessels, and DP support vessels, the author will contrast the levels of complexity in state of the art diesel electric

power systems against his experience with diesel hydraulic systems. The paper will address the technical issues,

cost issues and the human aspects with a focus on developing world markets.

Introduction

This paper is about simplicity. It deals with dynamic positioning only. It does not deal with mission equipment or

the power systems required for mission equipment. What I intend to do is layout a simple robust dynamic

positioning philosophy. This philosophy is appropriate for a drilling vessel, a pipelayer, a crane vessel, an

accommodation unit, or a rocket launch platform.

The idea for this paper came from two email conversations at the end of February 2013. The first of these

conversations was initiated by a request for input on experience with power management and generator controls

from competing vendors. The second was an inquiry from an owner who had been asked by his Naval Architect

why we didn’t take his Thrustmaster OD2000 portable thrusters apart then replace the couplings, gears, and

pumps with electric motors, a parallel switchboard and generators on the engines.

The first conversation spoke to the overall complexity of the systems we consider to be the state of the art today,

while in the second conversation I was hearing someone say we should do this because, “That is what we do.” I am

really more concerned about the latter. What I read between the lines was, here we have designers who are saying

”Okay you have this existing robust system you want to install, but it is not a diesel electric system so we should

tear it apart and spend a huge amount of money to rebuild it.” This begs the question, “Why would they suggest

that?” The most plausible answer is, because, ”That’s how DP2 works.” My contention is; that answer is wrong.

Background

My first experience with diesel hydraulic thrusters was on the reel barge Chickasaw at Global Industries in 1994.

Having at that time been involved in the construction of six diesel electric drilling rigs, two of which were full DP, I

approached the installation with a fair amount of skepticism. However, the installation on the Chickasaw was

highly successful and the units remain in service today.

While the Chickasaw was very successful, the concept of using diesel hydraulic systems for conversions and new

builds was never really on the radar again until 2001. We were approached to charter the Titan 2 and convert the

vessel to DP using diesel hydraulic thrusters. Once again the project was highly successful and the vessel and

thrusters remain in service today. The Titan 2 conversion was the subject of a paper at the MTS DP conference in

2002 by Keith Hebert entitled, “Maintaining Full Station Keeping Capabilities During a Blackout”

The Titan 2 conversion consisted of eight 1000 HP thrusters and a Kongsberg DP system. Since the vessel was

chartered, the project was designed to have the minimum impact on the hull with the minimum investment

possible in the vessel. I left Global in 2004 and went on to do a number of other diesel electric retrofits and new

builds before going into semi-retirement in 2008. I never thought at that time that I would be spending the twilight

years of my career doing diesel hydraulic conversions.



Since 2009 the two major projects I have been involved with have been the new builds of the Global 1200 / 1201

DP2 pipelayers and the conversion of the Truong Sa (Ex-Titan), sister ship to the Titan 2. The Global pipelayers are

diesel electric with MV busses capable of being used in a ring configuration. The Truong Sa has been converted to a

pipelayer with eight 2000 HP diesel hydraulic thrusters.

Presently I am working on a number of other conversions including the Titan 3 & 4, the McDermott DB30, as well

as a semi-submersible conversion to a work over rig. Thrustmaster now builds hydraulic thrusters up to 3000 HP.

The Diesel Electric Perspective

Beginning with the SeDco 445 in 1971, the first DP drilling vessels adopted diesel electric propulsion plants for a

number of reasons including:

Electrically driven thrusters were controllable.

The power plants were scalable. Power could be brought on line as needed.

They had an arguable level of redundancy.

At the time microprocessors were new to the market. Components in generator controls, switchboards, SCR

systems, shipboard I/C systems, etc. were primarily analog electronics or electrical devices. Digital controls were in

their infancy. Consequently, with the cost of automation high, only those processes which were deemed as

necessities were automated. Processing power was reserved for the DP system and power management systems.

While the first generation of DP systems was controlled by mini-computers, the second generation came online

with the advent of microprocessors and programmable logic controllers. The stage was set in the early 1980’s for a

revolution in industrial controls. Processing power became cheap and readily available.

The design paradigm set in the early days of DP drilling has proven to be durable. While the industry has evolved

from DC driven thrusters to AC driven thrusters, the basic idea of multiple generators on a common buss driving

redundant thrusters has become the standard for the majority of new build large DP vessels.

While the design paradigm remained more or less constant until the introduction of the ring buss, the availability

of cheap processing power and reliable data communications has created an environment in which everything that

can be automated will be. This has given rise to increasing levels of complexity.

The introduction of ring buss architecture in recent years has added further levels of complexity to installations.

Whereas a traditional DP2 six generator buss required the management of six generator breakers and a tie

breaker, a DP3 six generator ring buss will have six generator breakers and eight buss tie breakers with associated

protective relays, directional current sensors and power management scenarios.



The Evolution of Diesel Electric

By way of contrast, the following describes the evolution of a typical six generator, six thruster diesel electric

system. Switchgear on the earliest DP vessels was usually contained in one room, within one switchboard. In lieu of

a tie breaker, buss links were provided to split the buss.

With the introduction of DP2 regulations, a tie breaker was required. It was still possible to have one switchboard

built with the tie breaker in the buss. The board could therefore be installed in one switchgear room. One breaker

is added.



DP3 regulations made it necessary to place switchgear in separate rooms. As a result, two tie breakers were

required to protect the cables that connected the two switchboards. A second breaker is added.

A DP3 ring buss configuration requires the addition of eight breakers and associated protective relays.



Providing protection on a ring buss system requires directional protective relays.

Clearly these designs and the requisite testing have become vastly more complicated. Along with the added cost of

equipment, the coordination of the added breakers with the requirement for directional current control makes the

tuning and testing of these systems considerably more time consuming and expensive.

The Diesel Hydraulic Perspective

A Thrustmaster diesel hydraulic thruster consists of diesel driven HPU, a thruster unit and a remote control panel.

The HPU is fully self-contained including a fuel tank and controls. It can be either air cooled or water cooled

depending upon the installation. The thruster unit can be either a swing down unit, a retractable unit, or a hull

mounted unit.

These systems were originally designed for use as portable DP thrusters. They had swing down thrusters and

containerized air cooled HPUs. The conversion of the McDermott DB30 changed the game with the requirement

that the thrusters be retractable within the hull and the HPU’s installed below decks in the sponsons. In the case of

the DB30, there will be eight 2000 HP retractable thrusters and HPU’s installed. The DB30 and a number of other

pipelay / crane barges are good candidates for the addition of thrusters because many of them have been widened

with the addition of sponsons.



In contrast to the diesel electric units described earlier in this paper, the following is the complete one line diagram

for each individual thruster. There are five shipboard cables; 2 CAN bus, 1 six conductor signal cable and two

power cables. The CAN bus and 6 conductor are controls. The power cables are for the battery charger and the

emergency retraction pump for the thruster.

Since each HPU is totally self-contained, the units need only be connected to the sea chest valves for cooling water

and a fuel line to fill their tanks from the ships bunkers.

Upon completion, the DB30 will have eight totally independent thrusters located in segregated spaces. The only

interconnection between the thrusters will be fuel distribution to the HPU fuel tank and the control cabling from



the remote control panels to the DP system. Therefore, the design is simple, robust, and doesn’t require a high

degree of technical ability to operate and maintain.

The end result being that we will once again deliver a vessel that is capable of:

“Maintaining Full Station Keeping Capabilities During a Blackout”

Regulatory Complexity and Bias

As systems have become more complex, the regulatory environment has also become more complex. Beginning

with a single sentence in IMO Resolution A.649(16), DP regulations can now be measured by the pound of paper it

requires to print them.

Resolution A.649(16) 19 Oct. 1989

4.12 – Dynamic Positioning systems

Dynamic positioning systems used as a sole means of position keeping should provide a level of

safety equivalent to that provided for anchoring arrangements to the satisfaction of the

administration.

MSC 38.(63) 19 May 1994

*Reference is made to the Guidelines for Vessels with Dynamic Positioning approved by the

Maritime Safety Committee at its 63rd

session and disseminated by MSC/Circ. 645.

IMO MSC 645 6 June 1994 – 22 pages

DNV DYNPOS ER Jan 2011 – 33 pages

ABS EHS December 2012 – 80 pages

With the introduction of requirements the Failure Mode Effect Analysis, testing has become more rigorous. As

systems have become more complex, so have the FMEA requirements. Currently the regulatory bodies publish a

myriad of operational and design guidance documents.

In the recent past, both ABS and DNV have introduced new classifications for vessels design with “Enhanced

Reliability”. As seen in the following table from the Section 8 of the ABS Guide for Dynamic Positioning Systems

and the Part 6 Chapter 26 Section 5 of the DNV rules for ships, the new classifications would appear to apply only

to diesel electric propulsion.

While there was a clear need for the regulatory bodies to catch up to the state of the art in diesel electric systems,

there is an implicit bias toward the use of diesel electric power systems over any other form of propulsion. My

contention is that this contributes to the “That’s how DP2 works.” mindset.



A Thought Experiment

As defined by Wikipedia “Thought Experiment” from the German word “Gedankenexperiment”

The DB30 project and a follow on project to convert a semisubmersible drilling rig to a DP work over rig prompted

me to think about how a diesel hydraulic implementation would be incorporated in a new build and what types of

vessels would be appropriate for this DP paradigm.

The semisubmersible has existing sponsons. Locating the HPU in the sponsons is not practical, but an underwater

demountable hydraulic thruster is. Therefore on this project the plan is to place the HPUs on deck. Hydraulic

thrusters have no couplings, only hose connections. This makes the concept of an underwater demountable

hydraulic thruster appealing.

Having been associated with many of the people responsible for the design that evolved from the SeDco 600 to the

ENSCO 8500 series and having done a rig assessment on the ENSCO 8501 for the first post Macando GOM well, I

decided to use the 8500 as a baseline rig for this “Gedankenexperiment”.

The 8500 rigs evolved from the 600 rigs, which were small no frills anchored semis designed to be built on a panel

line. They had no tubulars, which made them cheaper to build than the 700 series rigs SeDco had been building.

The 600 design morphed into the ENSCO 7500, which was DP, and then to the ENSCO 8500.

The particulars from the ENSCO 8500 Brochure:

At first glance when I considered converting this design to a diesel hydraulic DP design, I thought that eight 3000

HP thrusters would not provide comparable power. After a second look, I realized I had fallen into a trap. I was

thinking diesel electric DP2. After all, “That’s how DP2 works.”

If the worst case failure is the loss of half the thrusters that would leave this vessel with 4 X 3,500 HP = 14,000 HP,

replacing the thrusters with 3000 HP diesel hydraulic thrusters with the worst case failure being loss of one

thruster leaves the vessel with 7 X 3,000 HP = 21,000 HP. In other words we go down in installed thruster power

8.57% and up in single point failure holding capability by 50%.



Let’s take a look at how I plan to do this. The columns on these vessels are 45’ X 50’. At the 79’ 6” level there is a

flat that holds the thruster transformers, VFD’s and MCC for auxiliaries. I’ll throw them all overboard and place two

diesel HPU’s on the flat. I will run the hydraulic piping external to the column down to my thruster and return it

through a keel cooler. That will manage the heat in the fluid. The engine will be cooled with the same heat

exchangers used on the McDermott project. Each column requires a sea chest for ballasting and each HPU has a

hydraulically driven cooling water pump. Provided that the CAT engine freshwater cooling pump can handle the

head requirements, the engines can be keel cooled eliminating the raw water pump and sea chest connection.

Since I now have four totally independent engine rooms, I am DP3 compliant. In DP3 mode, my worst case failure

is the loss of an engine room with two HPU’s. This leave me with 6 X 3,000 HP = 18,000 HP versus 4 X 3,500 =

14,000 HP. The result is an increase in holding power of 29% over the diesel electric rig.

So what have I just done? I lost 8 each switchboard cells, transformers and VFDs. I lost eight AC motors, and all the

required auxiliaries including MCC’s to drive fans, cooling water pumps, thruster steering gear, etc. I have lost

miles of cable, cable hangers, and associated penetrations. I have cleaned the main deck off by reducing the

generation requirements and, therefore, the engine room and switchgear room size. At the same time I have lost

piping diameter and pump capacity required to cool the mission equipment generation. I have lost weight,

equipment cost and construction cost. As a bonus, by losing weight and moving the thruster HPU’s to the column

flats, I have gained deck space, deck load and improved my VCG.



I will need to put the appropriate amount generation capacity onboard to run my mission equipment and hotel

services. Having removed the thruster load from the system, I expect to drop the voltage level from 4160 medium

voltage to 600 volts. This should lower the cost of the switchgear and generators. As noted earlier this paper does

not deal with installed power for mission equipment. We are looking at simplicity and “Enhanced Reliability” of DP

systems. Therefore I will leave it at that.

Having run through this thought experiment; I conclude that I can build a simple, highly reliable DP3 compliant

semisubmersible for a lower cost with more deck load and better stability characteristics on the same platform.

That was simple.

Efficiency

The question of efficiency is bound to come up. ”But isn’t diesel electric more efficient.” Is it? Since this is a paper

about simplicity, here is the simple answer. It’s all voodoo, like federal deficit predictions.

We know the BTU’s in a given volume of MDO. We know that the torque is imparted to the water at the propeller

tip. We know that the BTUs in the MDO are converted into torque at the flywheel by the diesel. We know there

are efficiency losses in any means of transmission for that torque to the propeller tip. Making a bunch of

assumptions we can calculate the losses in any form of transmission. What we don’t know is the amount of torque

we need for a given unit of time. In other words we cannot predict the environment. Consequently, all design

points are based upon assumptions. You see it’s kind of like the federal deficit predictions, voodoo.

I will leave the subject with my DP2 question. Over the life cycle of your equipment, is it cheaper to run two large

generators on either side of the tie breaker at 30% for extended periods than it is to run fewer directly driven

thrusters at 80% with your remaining capacity on standby? Since we know that it is all voodoo based upon

whatever assumptions you choose to make, please talk amongst yourselves. Like the federal deficit, it is not a

conversation I care to be involved in.

The Developing World

The Vietnamese have an offshore market with expectations for development in deep water. Operators are under

pressure from the Government to employ locals wherever possible. There is also pressure to build rigs and

equipment locally. My subjective observation is that the state of shipbuilding in Vietnam is roughly the same today

as the state of shipbuilding was in Korea in 1981 when we began to build the SeDco 711, 712, & 714. Steel goes

together fairly well. All things electrical are a big problem. There are cultural hurdles with project controls and

management.

We were converting the Truong Sa for an operator who let a design contract for two DP2 AHTS vessels. The vessels

will be conventionally shafted with direct diesel driven CP bow thrusters. The design is similar to the Harvey Gulf

vessels in use in the Gulf of Mexico. These are very successful, simple boats. They are also appropriate for the

capabilities of the Vietnamese workforce.

The operator is required by the government to build these boats at a yard that was bankrupt and has been taken

over by the state owned oil company. The yard has a huge graving dock and was designed to build super-tankers.

In fact there is one spread around the yard in modules, some assembly required. The yard is located on the coast

South of DaNang in an area that is an economic development zone. Dung Quat is a rural, primarily agricultural

area. The parallels with Korea in 1981 are striking. Back then Hyundai had the largest graving dock in the world in

Ulsan. They had to pay hardship pay to locals to work there because it was in a sparsely developed area.



While there have certainly been advances in the delivery system for educational materials, no one has yet figured

out how to deliver experience in any really new and creative way. The Vietnamese have very limited experience

with complex DP power systems. They intend to build deep water rigs in Vietnam and will face a steep learning

curve in doing so. The more complex the rig, the more steep the curve will be.

I use the example of Vietnam because of my recent experience there. Throughout the developing world the

industry faces the same problems. Pressure from local governments to employ nationals is not likely to abate in

the future. Educated and more importantly experienced locals are not going to just appear. They will have to be

developed. The more complex the systems we produce, the more risk we face.

There is a report by Wood Mackenzie sited on page 37 of the August 2013 Ocean News & Technology that states

the industry will need 95 new deep water rigs between 2016 and 2022. The report further states that rig

contractors will need an additional 37,000 workers over the next decade to operate the fleet. While this

forecasting of the future of our industry is based upon assumptions, like the federal deficit, we can be reasonably

assured that the need for qualified people in the offshore business is not likely to abate in the near term.

Conclusion

As with my initial reaction to diesel hydraulic propulsion systems, my reaction to early DP supply designs using

shaft generators was extremely negative when I first encountered them. The same was true of my opinion of direct

drive diesel boats. In both cases I thought they should just build a diesel electric boat. Having had the opportunity

to survey Chouest and Harvey Gulf vessels I recognize the virtues of these designs. As they have evolved, they have

become simple, robust and appropriate to the their missions.

There is a tendency for all of us to be predisposed to doing things the way we first learned how to do them. My

father drove Chevy’s, so I know that Chevy’s are the best car. I learned how to build diesel electric DP vessels from

my mentors and peers, so I know, ”That’s how DP2 works.” At least I used to know that. I now know better. I know

that simpler is better.

Scientific American, August 2013, page 86.

“Studies suggest that random mutations that individually have no effect on an organism can fuel the

emergence of complexity in a process known as constructive neutral evolution.”

While the above statement refers to a biological process, it is analogous to the positive feedback system that

drives the evolution of complexity between design and regulation.

Sound Bites

My Mantra: “Solutions should be elegant in their simplicity.”

Dr. Stanbery’s three engineering criteria: “It should work fine, fail safe, and last a real long time.”

dynamic positioning conference october 15-16,...

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